1. Field of the Invention
The present invention relates to an organic light-emitting device and a display apparatus.
2. Description of the Related Art
Organic light-emitting displays are known as one application of organic light-emitting devices. In order to realize an excellent organic light-emitting display that has a low power consumption, a high luminance, and a long service life, it is necessary to further improve the performance of materials constituting the organic light-emitting devices. On the other hand, a manufacturing method based on a coating process using a polymer material or the like enables cost reduction of organic light-emitting displays. A manufacturing method based on such a coating process is presently the main method for manufacturing organic light-emitting displays.
However, a problem associated with organic light-emitting devices using polymer materials is that the element operation life is shorter than that of low-molecular weight organic light-emitting devices. Polymer materials are typically synthesized by polymerizing a monomer of one kind or monomers of several kinds and the polymer materials obtained tend to have a broad molecular weight distribution and are therefore very difficult to manufacture accurately. This is the main factor affecting the device operation life.
Yet another problem is that the flatness and electronic properties of thin films of polymer materials vary significantly depending on the particular method selected employed for forming the films and the specific treatment conditions.
An attempt to improve the device operation life by using a dendrimer with a medium molecular weight that is disclosed in Japanese Patent Laid-open No. 2003-231692 represents a method for overcoming the drawbacks inherent to the above-described polymer materials. Further, an increase in emission efficiency can be attained by using a polyfluorene of a medium molecular weight (oligofluorene) in which the 2-position and the 7-position serve as connection positions.
Concerning oligofluorenes, a review of optical excitation of oligofluorene compounds of a π-stacking type connected to each other in 9-positions has been reported in J. Am. Chem. Soc., 125, 15474 (2003). However, organic light-emitting devices using bisfluorene compounds connected to each other at 9-positions have not yet been reported.